Cancer is a leading cause of mortality worldwide. Traditional regimens of cancer management have been successful in the management of a selective group of circulating and solid cancers. However, many tumors are resistant to traditional approaches. In recent years, immunotherapy for the treatment of cancers has been explored, which involves the generation of an active systemic tumor-specific immune response of host origin by administering a vaccine composition at a site distant from the tumor. Various types of vaccines have been proposed, including those containing isolated tumor-associated antigens.
Prostate cancer is the second most commonly diagnosed cancer and the fourth leading cause of cancer-related death in men in the developed countries worldwide. Various prostate-associated antigens (PAA), such as prostate-specific antigen (PSA), prostate-specific membrane antigen (PSMA), and prostate stem cell antigen (PSCA) have been shown to be overexpressed by prostate cancer cells as compared to normal counterparts. These antigens, therefore, represent possible targets for inducing specific immune responses against cancers expressing the antigens via the use of vaccine-based immunotherapy. (see e.g. Marrari, A., M. Iero, et al. (2007). “Vaccination therapy in prostate cancer.” Cancer Immunol Immunother 56(4): 429-45.)
PSCA is a 123-amino acid membrane protein. The amino acid sequence of the full length human PSCA consists of amino acids 4-123 of SEQ ID NO:21. PSCA has high tissue specificity and is expressed on more than 85% of prostate cancer specimens, with expression levels increasing with higher Gleason scores and androgen independence. It is expressed in 80-100% of bone metastasis of prostate cancer patients.
PSA is a kallikrein-like serine protease that is produced exclusively by the columnar epithelial cells lining the acini and ducts of the prostate gland. PSA mRNA is translated as an inactive 261-amino acid prepropSA precursor. PrepropSA has 24 additional residues that constitute the pre-region (the signal polypeptide) and the propolypeptide. Release of the propolypeptide results in the 237-amino acid, mature extracellular form, which is enzymatically active. The amino acid sequence of the human full length PSA is provided in SEQ ID NO: 15. PSA is organ-specific and, as a result, it is produced by the epithelial cells of benign prostatic hyperplastic (BPH) tissue, primary prostate cancer tissue, and metastatic prostate cancer tissue.
PSMA, also known as Folate hydrolase 1 (FOLH1), is composed of 750 amino acids. The amino acid sequence of the human full length PSMA is provided in SEQ ID NO:1. PSMA includes a cytoplasmic domain (amino acids 1-19), a transmembrane domain (amino acids 20-43), and an extracellular domain (amino acids 44-750). PSMA is a type II dimeric transmembrane protein expressed on the surface of prostate cancer cells and on neovasculature. It is also expressed on normal prostate cells, brain, salivary gland and biliary tree. However, in prostate cancer cells it was found to be expressed at 1000-fold higher levels than normal tissues. It is abundantly expressed on neovasculature of a variety of other solid tumors such as colon, breast, liver, bladder, pancreas, lung, renal cancers as well as melanoma and sarcomas. Thus, PSMA is considered a target not only specific for prostate cancer cells but also a pan-carcinoma target for other cancers. The expression of PSMA appears to be a universal feature of prostate carcinomas and its increased expression correlates with tumor aggressiveness. PSMA expression is highest in high-grade tumors, metastatic lesions and androgen-independent disease.
While a large number of tumor-associated antigens have been identified and many of these antigens have been explored as protein-based or DNA-based vaccines for the treatment or prevention of cancers, most clinical trials so far have failed to produce a therapeutic product. One of the challenges in developing cancer vaccines resides in the fact that the cancer antigens are usually self-derived and, therefore, poorly immunogenic because the immune system is self-regulated not to recognize self-proteins. Accordingly, a need exists for a method to enhance the immunogenicity or therapeutic effect of cancer vaccines.
Numerous approaches have been explored for enhancing the immunogenicity or enhancing anti-tumor efficacy of cancer vaccines. One of such approach involves the use of various immune modulators, such as TLR agonists, TNFR agonists, CTLA-4 inhibitors, and protein kinase inhibitors.
Toll-like receptors (TLRs) are type 1 membrane receptors that are expressed on hematopoietic and non-hematopoietic cells. At least 11 members have been identified in the TLR family. These receptors are characterized by their capacity to recognize pathogen-associated molecular patterns (PAMP) expressed by pathogenic organisms. It has been found that triggering of TLR elicits profound inflammatory responses through enhanced cytokine production, chemokine receptor expression (CCR2, CCR5 and CCR7), and costimulatory molecule expression. As such, these receptors in the innate immune systems exert control over the polarity of the ensuing acquired immune response. Among the TLRs, TLR9 has been extensively investigated for its functions in immune responses. Stimulation of the TLR9 receptor directs antigen-presenting cells (APCs) towards priming potent, TH1-dominated T-cell responses, by increasing the production of pro-inflammatory cytokines and the presentation of co-stimulatory molecules to T cells. CpG oligonucleotides, ligands for TLR9, were found to be a class of potent immunostimulatory factors. CpG therapy has been tested against a wide variety of tumor models in mice, and has consistently been shown to promote tumor inhibition or regression.
Cytotoxic T-Lymphocyte Antigen 4 (CTLA-4) is a member of the immunoglobulin superfamily and is expressed on the surface of Helper T cells. CTLA-4 is a negative regulator of CD28 dependent T cell activation, and acts as an inhibitory checkpoint for the adaptive immune response. Similar to the T-cell costimulatory protein CD28, CTLA-4 binds to CD80 and CD86 on antigen-presenting cells. CTLA-4 transmits an inhibitory signal to T cells, whereas CD28 transmits a stimulatory signal. Human antibodies against human CTLA-4 have been described as immunostimulation modulators in a number of disease conditions, such as treating or preventing viral and bacterial infection and for treating cancer (WO 01/14424 and WO 00/37504). Various preclinical studies have shown that CTLA-4 blockade by monoclonal antibodies enhances the host immune response against immunogenic tumors, and can even reject established tumors. Two fully human anti-human CTLA-4 monoclonal antibodies (mAbs), ipilimumab (MDX-010) and Tremelimumab (also known as CP-675206), have been investigated in clinical trials in the treatment of various types of solid tumors.
The tumor necrosis factor (TNF) superfamily is a group of cytokines that engage specific cognate cell surface receptors, the TNF receptor (TNFR) superfamily. Members of the tumor necrosis factor superfamily act through ligand-mediated trimerization, causing recruitment of several intracellular adaptors to activate multiple signal transduction pathways, such as apoptosis, NF-kB pathway, JNK pathway, as well as immune and inflammatory responses. Examples of the TNF Superfamily include CD40 ligands, OX40 ligands, 4-1BB ligands, CD27, CD30 ligand (CD153), TNF-alpha, TNF-beta, RANK ligands, LT-alpha, LT-beta, GITR ligands, and LIGHT. The TNFR Superfamily includes, for example, CD40, OX40, 4-1BB, CD70 (CD27 ligand), CD30, TNFR2, RANK, LT-beta R, HVEM, GITR, TROY, and RELT. CD40 is found on the surface of B lymphocytes, dendritic cells, follicular dendritic cells, hematopoietic progenitor cells, epithelial cells, and carcinomas. CD40 binds to a ligand (CD40-L), which is a glycoprotein and expressed on activated T cells, mostly CD4+ but also some CD8+ as well as basophils/mast cells. Because of the role of CD40 in innate and adaptive immune responses, CD40 agonists, including various CD40 agonistic antibodies, such as the fully human agonist CD40 monoclonal antibody CP870893, have been explored for usage as vaccine adjuvants and in therapies.
Protein kinases are a family of enzymes that catalyze the phosphorylation of specific residues in proteins. Protein kinases are key elements in signal transduction pathways responsible for transducing extracellular signals, including the action of cytokines on their receptors, to the nuclei, triggering various biological events. The many roles of protein kinases in normal cell physiology include cell cycle control and cell growth, differentiation, apoptosis, cell mobility and mitogenesis. Kinases such as c-Src, c-Abl, mitogen activated protein (MAP) kinase, phosphotidylinositol-3-kinase (PI3K) AKT, and the epidermal growth factor (EGF) receptor are commonly activated in cancer cells, and are known to contribute to tumorigenesis. Logically, a number of kinase inhibitors are currently being developed for anti-cancer therapy, in particular tyrosine kinase inhibitors (TKIs): cyclin-dependent kinase inhibitors, aurora kinase inhibitors, cell cycle checkpoint inhibitors, epidermal growth factor receptor (EGFR) inhibitors, FMS-like tyrosine kinase inhibitors, platelet-derived growth factor receptor (PDGFR) inhibitors, kinase insert domain inhibitors, inhibitors targeting the PI3K/Akt/mTOR pathway, inhibitors targeting the Ras-Raf-MEK-ERK (ERK) pathway, vascular endothelial growth factor receptor (VEGFR) kinase inhibitors, c-kit inhibitors and serine/threonine kinase inhibitors. A number of kinase inhibitors have been investigated in clinical investigation for use in anti-cancer therapies, which includes, for example, MK0457, VX-680, ZD6474, MLN8054, AZD2171, SNS-032, PTK787/ZK222584, Sorafenib (BAY43-9006), SU5416, SU6668 AMG706, Zactima (ZD6474), MP-412, Dasatinib, CEP-701, (Lestaurtinib), XL647, XL999, Tykerb, (Lapatinib), MLN518, (formerly known as CT53518), PKC412, ST1571, AMN107, AEE 788, OSI-930, OSI-817, Sunitinib malate (Sutent; SU11248), Vatalanib (PTK787/ZK 222584), SNS-032, SNS-314 and Axitinib (AG-013736). Gefitinib and Erlotinib are two orally available EGFR-TKIs.
The immune modulators that have been explored are typically administered systemically to the patients, for example, by oral administration, intravenous injection or infusion, or intramuscular injection. One major factor that limits the effective use of some of the immune modulators is toxicity caused by high systemic exposure to the administered agents. For example, with respect to CD40 agonists, it has been reported that 0.3 mg/kg is the maximum tolerated dose for an exemplified agonistic CD40 antibody and that higher doses may elicit side effects including venous thromboembolism, grade 3 headache, cytokine release resulting in toxic effects such as chills and the like, and transient liver toxicity. (Vanderheide et al., J. Clin. Oncol. 25(7): 876-8833 (March 2007). In a clinical trial to investigate combinations of intravenous Tremelimumab (an anti-CTLA-4 antibody) plus oral sunitinib in patients with metastatic renal cell carcinoma, rapid onset of renal failure was observed and, as a result, further investigation of Tremelimumab at doses higher than 6 mg/kg plus sunitinib at 37.5 mg daily was not recommended. See: Brian I. Rini et al.: Phase 1 Dose-Escalation Trial of Tremelimumab Plus Sunitinib in Patients With Metastatic Renal Cell Carcinoma. Cancer 117(4)158-767 (2011)]. Therefore, there is a need for vaccine-based immunotherapy regimens where the immune modulators are administered at effective doses which do not elicit severe adverse side effects such as liver toxicity or renal failure.